Neurofibromatosis, type I (NF1), is inherited as a dominant trait, and is extremely common, affecting approximately one in every 3,500 individuals worldwide. The disorder is highly variable in its clinical presentation, and only one-third of affected individuals develop medical complications severe enough to require intervention. It is not known if specific mutations of the NF1 gene are associated with specific clinical presentations. The objective of this protocol is to determine if patients with similar clinical syndromes have similar NF1 mutations. Because some NF1 patients develop malignant changes in their previously benign neurofibromas, Dr. Viskochil is attempting to identify additional mutations as tumors progress from benign to malignant. These studies are being done in cooperation with Dr. Jan Friedman at the University of British Columbia.